Ll. Pech, REGULATION OF CILIARY MOTILITY IN PARAMECIUM BY CAMP AND CGMP, Comparative biochemistry and physiology. Part A, Physiology, 111(1), 1995, pp. 31-37
Paramecium tetraurelia is a useful model system for the study of signa
l transduction mechanisms that couple changes in membrane potential to
changes in ciliary motility, and cAMP and cGMP have been implicated a
s second messengers in this system. Changes in ciliary beat are correl
ated with changes in the membrane potential, V-m, with hyperpolarizati
ons resulting in increased beat frequency and increased forward swimmi
ng speed. The intercellular levels of cAMP and cGMP vary with V-m, and
increasing internal cAMP by microinjection or the use of membrane per
meant analogs results in increased swimming speed. In addition, cAMP a
nd cGMP modify the swimming behavior of permeabilized Paramecium, and
the sensitivity of cilia to cAMP and cGMP depends upon the location of
the cilia on the cell surface. However, increasing internal cAMP also
results in hyperpolarization and increasing internal cAMP does not ov
erride the effect of V-m. These results have lead to two conflicting m
odels to describe the role of cAMP: (1) stimulus --> hyperpolarization
of V-m --> increased [cAMP](in) --> increased beat frequency, and (2)
stimulus --> increased [cAMP](in) --> hyperpolarization of V-m --> in
creased beat frequency. This review discusses the data that support th
ese models and possible experimental approaches to resolve the paradox
presented by these models.